The present invention relates to a process and an apparatus for coating the surfaces of containers with a material.
Nowadays coating materials of, for example, plastics are often applied on the surfaces of containers, e.g. glass bottles for soft drinks, in order to strengthen the containers so that they can be used repeatedly without the risk of breakage. Such coating of containers has been conventionally conducted mainly either by spraying a coating material in a powdery state onto the container or by dripping the containers in a liquid medium containing a coating material. However, these methods are disadvantageous in that it is very difficult for them to control the thickness of coating layer.
As a way for overcoming such disadvantage, it has been proposed to apply a liquid coating on the surfaces of containers by means of nozzles. This method using nozzles makes it possible to obtain a relatively homogenous coating and also to carry out the coating for a number of containers continuously. More particularly, a plurality of containers can be successively applied on the surfaces thereof with a coating material by being successively transported into a coating zone and being applied with the material by means of the nozzles in the zone.
However, this method has the drawback that a sophisticated mechanism is needed for the action of the nozzles in the coating zone. For example, in the method most commonly employed, there is required a precise mechanism by which nozzles can move to exactly follow a container being transported horizontally in the coating zone and then move backward (i.e. in the direction opposite to the direction of the transportation of the containers) in order to commence the coating of a subsequent container (See Japanese Patent Application Publication No. 7091/1982). Thus, in addition to the need for a complex mechanism for controlling the movement of nozzles, the method suffers from a further disadvantage that, as the nozzles are being moved backward, some of the liquid coating material will drip from the nozzles without being applied onto containers. For avoiding the loss of the liquid coating material by the dripping during the backward movement of the nozzles, there has been proposed a means for temporarily stopping the supply of the liquid coating material and sucking back the material, at the time when each nozzle has finished applying the coating onto a given container (Japanese Patent Application Public Disclosure No. 139858/1980). However, such an approach is not preferable from the operational standpoint in that the supplying means for the liquid coating material has to be forced to function against its intrinsic action. In addition, in spite of the attempt to suspend the supply of the liquid coating material by the above-mentioned means, it is impossible to completely prevent the dripping of the material. Problems also arise in that due to the temporary stopping of the supply of the material there occurs clogging of the nozzles with the material and further there is difficulty in producing a homogeneous coating on containers with the material when the supply of the material is re-started.